Saturn Forms Night Sky Triangles With Stars and Moon

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If you're outside soon after it gets sufficiently dark to see the
stars this week, you may notice a large and slender isosceles
triangle high in the southern sky. The triangle appears tipped to
the left, with the vertex poised high above the base; the
triangle itself seems to be pointing toward the point directly
overhead (called the zenith).

With the official start of summer in the Northern Hemisphere
right around the corner, you might think that you are looking at
the famous Summer Triangle. But no … that particular pattern of
three bright stars is only now emerging into view, low in the
east-northeast. [ Sky
map: Saturn Sky Triangle in June ]

So what is this other eye-catching triangle of three bright
stars?

Two stars … one Saturn

Actually ... only two of the three stars in the prominent
isosceles triangle are stars. One of the "stars" is actually a
planet! And as a result, this triangular pattern will appear to
alter its shape in the weeks and months to come.

The planet in question is Saturn
and it appears to glow a sedate yellow-white as one of the two
“stars” in the base of the triangle. The other object is the
bluish star Spica, in the constellation Virgo; Spica is on the
left while Saturn is on the right. [ Photos:
The Rings and Moons of Saturn ]

Saturn's rings,
visible in any telescope magnifying at least 30-power, are
currently tilted 7.3 degrees, the smallest for this year. In the
course of the next six years the rings will gradually "open out,"
eventually reaching a maximum tilt toward Earth in October
2017.

The third star in the triangle is the brilliant yellow-orange
Arcturus in the constellation, Boötes. The triangle will remain
in view until around 2 a.m. local time. By then, Saturn and Spica
will be low on the west-southwest horizon and will soon
set. Arcturus will remain in view, however, until the break
of dawn.

On June 13, Saturn
will seem to come to a halt against the background stars as it's
retrograde or "backwards motion" comes to an end. Since late
January, Saturn has been plodding slowly to the west, but after
June 13 it will reverse course and start moving to the east
toward Spica.

That means that the base of the triangle will be getting smaller
and the triangle itself will appear to get narrower as the summer
progresses.

By late September,
Saturn and Spica will be getting too low in the western
evening sky and too deeply immersed in the evening twilight to be
seen. When they again become visible, it will be during early
November, low in the east-southeast before sunrise.

But now, the Saturn-Spica-Arcturus pattern will no longer
resemble a triangle, but rather more of a straight line.

That pretty much will be the case through next year, but two
years from now, in the late spring and summer of 2013, our
attractive isosceles triangle will return. Except Saturn and
Spica will have exchanged their positions in the base of the
triangle and the triangle itself will seem to be tipped to the
right, not the left.

Moon joins sky triangle party

And if you can't get enough of triangles in our current evening
sky, be sure to check out the scene soon after sunset on Friday
(June 10), when
the moon joins the show.

The apparent distances between objects in the night sky can be
measured in terms of degrees. Your clenched fist held at arm's
length, for example, could cover about 10 degrees of arc.

On Friday, Saturn will be high in the south-southwest at dusk and
will appear to form a rather broad triangle with the waxing
gibbous moon, about 10 degrees below it and Spica, about 15
degrees to Saturn's lower left.

Joe Rao serves as an instructor and guest lecturer at New
York's Hayden Planetarium. He writes about astronomy for The New
York Times and other publications, and he is also an on-camera
meteorologist for News 12 Westchester, N.Y.